Today, most dental crowns and bridges are produced by a process which employs metal alloys and dental porcelains. The alloy frames, usually referred to as "copings", are prepared by the lost wax investment casting process. A variety of dental porcelains are then applied to the coping. The porcelain simulates the natural tooth both functionally and esthetically, and is ordinarily applied in two stages. First, an opaque porcelain layer (which is used to mask the coping) is applied as an aqueous paste to the surface of the metal coping, and this opaque layer is then dried and fired. Additional opaque porcelain is sometimes applied, dried, and fired if the initial application is either non-uniform or does not completely mask the alloy substructure. Once the opaque porcelain has been satisfactorily applied, the body porcelain layers, usually a gingival and an incisal porcelain, are applied as aqueous pastes and then dried and fired. A minimum of two firings is required; this includes a minimum of one firing for the opaque porcelain layer and a minimum of one firing for the body porcelain layers.
Recently, all-ceramic dental restorations have been introduced commercially. For instance, see Starling et al., U.S. Pat. No. 4,265,669. In an all-ceramic dental restoration, the metal coping is replaced with a ceramic base. In many cases, several layers of porcelain will be applied on top of the ceramic base. For instance, the ceramic base may be colored by application of a layer of a porcelain stain or by application of a layer of a pigmented dentino porcelain. In either case, one or more body porcelain layers will be applied on top of the stain or the dentino porcelain. Again, it is the usual practice to fire the restoration after the application of each layer, and as is the case with metal-based restorations, at least two firings are therefore needed; one for the stain or dentino porcelain and at least one for the body porcelain(s).
This invention provides a dental porcelain paste composition that does not have to be fired prior to the application of subsequent porcelain layers. As a result, both time and energy can be saved by practicing this invention since at least one firing procedure can be eliminated during the process for producing a dental crown or bridge.